To use in Observable,

whileAsync=require('https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-while@umd/browser.js')

To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:

varwhileAsync=require('path/to/vendor/umd/utils-async-while/index.js')

To include the bundle in a webpage,

<scripttype="text/javascript"src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-while@umd/browser.js"></script>

If no recognized module system is present, access bundle contents via the global scope:

<scripttype="text/javascript">(function(){window.whileAsync;})();</script>

Invokes afunction until apredicate function returnsfalse.

functionpredicate(i,clbk){clbk(null,i<5);}functionfcn(i,next){setTimeout(onTimeout,0);functiononTimeout(){console.log('beep: %d',i);next();}}functiondone(error){if(error){throwerror;}}whileAsync(predicate,fcn,done);/* =>    beep: 0    beep: 1    beep: 2    beep: 3    beep: 4*/

Thepredicate function is provided two arguments:

• i: iteration number (starting from zero).
• clbk: a callback indicating whether to invokefcn.

Theclbk function accepts two arguments:

• error: error object.
• bool: test result.

If the test result is truthy, the function invokesfcn; otherwise, the function invokes thedone callback.

The function to invoke is provided two arguments:

• i: iteration number (starting from zero).
• next: a callback which must be invoked before proceeding to the next iteration.

The first argument of bothclbk andnext is anerror argument. If either function is called with a truthyerror argument, the function suspends execution and immediately calls thedone callback for subsequenterror handling.

functionpredicate(i,clbk){clbk(null,i<5);}functionfcn(i,next){setTimeout(onTimeout,0);functiononTimeout(){next(newError('beep'));}}functiondone(error){console.error(error.message);// => beep}whileAsync(predicate,fcn,done);

Thedone callback is invoked with anerror argument and any arguments passed to the finalnext callback.

functionpredicate(i,clbk){clbk(null,i<5);}functionfcn(i,next){setTimeout(onTimeout,0);functiononTimeout(){next(null,i);}}functiondone(error,result){if(error){throwerror;}console.log(result);// => 4}whileAsync(predicate,fcn,done);

To set the function execution context for the invoked function, provide athisArg.

functionpredicate(i,clbk){clbk(null,i<5);}functionfcn(i,next){this.count+=1;setTimeout(onTimeout,0);functiononTimeout(){next();}}varcontext={'count':0};whileAsync(predicate,fcn,done,context);functiondone(error){if(error){throwerror;}console.log(context.count);// => 5}

• Execution isnot guaranteed to be asynchronous. To guarantee asynchrony, wrap thedone callback in a function which either executes at the end of the current stack (e.g.,nextTick) or during a subsequent turn of the event loop (e.g.,setImmediate,setTimeout).

• @stdlib/utils-async/do-until:invoke a function until a test condition is true.
• @stdlib/utils-async/do-while:invoke a function while a test condition is true.
• @stdlib/utils-async/until:invoke a function until a test condition is true.
• @stdlib/utils-while:invoke a function while a test condition is true.

This package is part ofstdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to developstdlib, see the main projectrepository.

SeeLICENSE.

Copyright © 2016-2025. The StdlibAuthors.